Understanding "at"

Many a times we need to schedule a task for a future time, say in the evening at 8 P.M. on a specific day. We can use the at command in such a situation.

Sometimes we need to repeat the same task at a specific time, periodically, every day, or every month. In such situations, we can use the crontab command.

Let's learn more about the utility of the at command. To use the at command, the syntax is as follows:

$ at time date

The following are the examples of the at command:

• The Control + D command will save the at job. The task will be executed at 11.15 A.M. This command will log messages to the log.txt file at 11.15 A.M.:

  $ at 11.15 AM
  at > echo "Hello World" > $HOME/log.txt
  at > Control + D
  

• The following command will send an e-mail on March 31, 2015 at 10 A.M.:

  $ at 10am mar 31 2015
  at> echo "taxes due" | mail jon
  at> ^D
  

• The following command will make the task run on May 20 at 11 A.M.:

  $ at 11 am may 20
  

• All the jobs which are scheduled by the at command can be listed using the following command:

  $ atq
  

• To remove a specific job listed by the atq command, we can use the following command:

  $ atrm job-id